Users, such as companies and the like, utilize storage controllers to manage data. The storage controller forms a logical volume on a storage area on the basis of RAID (Redundant Array of Independent Disks). This logical volume is provided to a host computer (hereinafter, host).
The amount of data being used by users is increasing on a daily basis, and volume sizes established to meet the situation as it stands now do not provide enough capacity. By contrast, in cases where the volume size is set larger than the size currently required in anticipation of increases in data, many unnecessary disk drives are present which raises costs.
Accordingly, technologies for preparing a virtual logical volume and allocating a real storage area to the virtual logical volume in accordance with actual use have been proposed (Patent Literature 1 and Patent Literature 2). Furthermore, in order to prevent the uneven distribution in a specific real volume of real storage areas that have been allocated to the virtual logical volume, technology for reallocating data is also known (Patent Literature 3).